Thermodynamic Inhibitors Research Articles

The Effect of Acidic Gases and Thermodynamic Inhibitors on the Hydrates Phase Boundary of Synthetic Malaysia Natural Gas

In this work, PVTSim was used to predict the hydrate phase equilibrium boundaries of a Malaysia synthetic natural gas (SNG) composition with increasing CO2 and H2S compositions in the presence of commonly used hydrate thermodynamic inhibitors such as methanol (MeOH), ethanol (EtOH), mono-ethylene glycol (MEG), diethylene glycol (DEG), tri-ethylene glycol (TEG). The increasing CO2 and H2S concentrations studied ranged from 5 – 50 mol%, while the inhibitors were tested at 10 wt%. To validate the accuracy of PVTSim, a validation test was conducted by predicting the phase behavior of a natural gas in the open literature. The predicted results were in good agreement with the literature data with a percentage deviation of 0.08% from the experimental data. From the predicted hydrate phase equilibrium for pure SNG field, it was found that, when the SNG composition was modified, the hydrate formation region shrank at increasing CO2 composition, reducing the hydrate formation risk whereas the hydrate formation region expanded at increasing H2S composition, increasing the hydrate formation threat. TEG was found to best inhibit hydrate formation in the studied gas compositions.

Combined Inhibition Effect of 1-Ethyl-3-methy-limidazolium Chloride + Glycine on Methane Hydrate

Ionic liquids and amino acids are recently introduced as novel gas hydrate inhibitors. However, they show less inhibition impact as compared to commercial gas hydrate inhibitors. Therefore, testing the combined effort of some of the best performed ionic liquids and amino acids in open literature would be necessary to understand and probably increase their inhibition performance. In this study, the synergic thermodynamic inhibition effect of 1-Ethyl-3-methy-limidazolium chloride (EMIM-Cl) + glycine on methane hydrate is reported. A sapphire hydrate cell and the T-cycle method was used within the pressures and temperatures ranges of 3 - 11 MPa and 274 – 286 K, respectively. Surprisingly the inhibition preformation of the mixed 1-Ethyl-3-methy-limidazolium chloride + glycine at 10 wt.% was found to be slightly less than pure 1-Ethyl- 3-methy-limidazolium chloride and glycine at same concentration, the results were all found to generally be in the same range with their pure systems (pure 1-Ethyl-3-methy-limidazolium chloride and glycine at 10wt%) . This behaviour is probably due to the colligative properties of 1- Ethyl-3-methy-limidazolium chloride and glycine, thus, causing a relatively equal inhibition impact.

A Generalized Correlation for Predicting Ethane, Propane, and Isobutane Hydrates Equilibrium Data in Pure Water and Aqueous Salt Solutions.

Hydrate formation can cause serious problems in hydrocarbon exploration, production, and transportation, especially in deepwater environments. Hydrate‐related problems affects the integrity of the deepwater platforms, leads to equipment blockages, and also increases operational costs. In order to solve these problems, salts are used as thermodynamic inhibitors and also mixed with the drilling fluids in most drilling processes. A comprehensive understanding of hydrate formation in aqueous salt solutions is vital to overcome these problems. Statistical thermodynamic models are commonly used to predict hydrate formation conditions in different aqueous solutions. However, these models involve rigorous computations and are restricted to certain conditions. They give inaccurate predictions of hydrate equilibrium conditions for high‐temperature, high‐pressure, and high‐salinity systems. Therefore, it is paramount to develop a simple‐to‐use and reliable prediction tool. In this work, an empirical correlation is developed and successfully used to predict the equilibrium conditions of ethane, propane, and isobutane hydrates in pure water and aqueous solutions of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride. Experimental data on hydrate formation conditions for these components are regressed and a generalized correlation is obtained. The predictions in this work show excellent agreement with all the experimental data in the literature.

A short review on natural gas hydrate, kinetic hydrate inhibitors and inhibitor synergists

Gas hydrate-caused pipeline plugging is an industrial nuisance for petroleum flow assurance that calls for technological innovations. Traditional thermodynamic inhibitors such as glycols and inorganic salts suffer from high dosing, environmental unfriendliness, corrosiveness, and economical burden. The development and use of kinetic hydrate inhibitors (KHIs), mostly polymeric compounds, with their inhibiting effects on hydrate nucleation and growth are considered an effective and economically viable chemical treatment for hydrate prevention. However, the actual performance of a KHI candidate is dependent on various factors including its chemical structure, molecular weight, spatial configuration, effective concentration, pressure and temperature, evaluation methods, use of other additives, etc. This review provides a short but systematic overview of the fundamentals of natural gas hydrates, the prevailing categories of polymeric kinetic hydrate inhibitors with proposed inhibition mechanisms, and the various synergists studied for boosting the KHI performance. Further research endeavors are in need to unveil the KHI working modes under different conditions. The conjunctive use of KHIs and synergists may facilitate the commercial application of effective KHIs to tackle the hydrate plugging problem in the oil and gas flow assurance practices.

The Effect of Atmospheric Electromagnetic Radiation on an Opened System

Abstract In opened systems with liquid-phase (for example open-source bioreactors for various purposes) very significant temperature can be generated. The operation of the system can be impaired, possibly completely inhibited (too low, too high temperature values). The analytic description of the operation’s heat flow is needed to achieve the optimized operation and to block the thermodynamic inhibition. The aim is to examine the inner system opportunities and the auxiliary energy. The estimates values quantify the effects of atmospheric electromagnetic radiation on opened systems. Based on the developed model by increasing the complexity of the method, it is appropriate to describe the heat flow of opened systems and to explore the energy integration possibilities.

Experimental study and thermodynamic modeling of the stability conditions of methane clathrate hydrate in the presence of TEACl and/or BMIM-BF4 in aqueous solution

In this work, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) and tetra ethyl-ammonium chloride (TEACl) were investigated to study their effects on thermodynamic stability conditions of methane clathrate hydrate. Different BMIM-BF4 and TEACl aqueous solutions (4.77 wt% (0.57 mol%) TEACl + 4.85 wt% (0.43 mol%) BMIM-BF4, 9.15 wt% (0.20 mol%) TEACl + 9.38 wt% (0.90 mol%) BMIM-BF4 and 11.82 wt% (1.63 mol%) TEACl + 11.82 wt% (1.20 mol%) BMIM-BF4) were used as thermodynamic inhibitors which have not been reported in literature. The experiments were conducted at constant volume from 274.6 K to 283.4 K and 3.18 MPa to 7.93 MPa. Moreover, methane hydrate phase equilibria in the aforementioned ioinic liquids (ILs) aqueous solutions were modeled. For this purpose, the chemical potential of water in hydrate phase is calculated using the van der Waals–Platteeuw (vdWP) theory. The Peng-Robinson (PR) equation of state (EoS) is used for calculation of fugacity in the gas phase. Water activity in the aqueous phase is determined by the NRTL activity coefficient model. Successful comparison of the experimental data with the modeling results confirms the model accuracy. It can also be observed that mixtures of the two aforementioned ionic liquids can inhibit methane hydrate formation more than each of single ILs. Furthermore, the studied ILs inhibit methane hydrate formation more at higher pressures.

Morphology Study on the Effect of Thermodynamic Inhibitors during Methane Hydrate Formation in the Presence of NaCl

In this study, we investigate the morphology of methane hydrate formation and growth in the presence of well-known thermodynamic inhibitors, monoethylene glycol (MEG) and methanol (MeOH) in a quiescent system. Morphology changes observed during the growth of methane hydrate while employing 5 wt % MEG and MeOH solutions in the presence and absence of NaCl are presented. When 5 wt % of MEG or MeOH was present in an aqueous solution individually, hydrate grew predominantly within the bulk solution featuring a “ridge”-shaped formation above the interface. In the presence of 3.5 wt % NaCl, an enhanced inhibition was observed for methane hydrates formed from 5 wt % MEG solution with limited hydrate growth in the bulk solution and above the gas-liquid interface. In contrast, 5 wt % MeOH solution in the presence of 3.5 wt % NaCl resulted in an increased hydrate growth in bulk (compared to the system without NaCl) and on the reactor wall above the gas–liquid interface, implying a weak promotion rather than the inh...

New methane hydrate phase boundary data in the presence of aqueous amino acids

Currently there are few amino acids hydrate based thermodynamic studies compared to kinetic studies, thus, the thermodynamic effect of four amino acids on methane hydrate formation are presented herein. The amino acids (valine, threonine, asparagine, and phenylalanine) were tested as gas hydrate inhibitors using the isochoric pressure search method in a high pressure stirring reactor. They were tested at 1 wt% and 5 wt% in the temperature and pressure ranges of 275.71–286.10 K and 3.52–10.25 MPa, respectively. All studied amino acids thermodynamically inhibited methane gas hydrate formation, with valine exhibiting the best inhibition impact with an average depression temperature of 0.529 K at 5 wt%. Amino acids side chain properties were found to cause the variations in their inhibition impact. This study is useful to fully understand the thermodynamic inhibition effect of amino acids on gas hydrate formation. Inferring from the results in this study and literature, amino acids are thermodynamic gas hydrate inhibitors, while most of them are kinetic promoters.

Universal correlation for gas hydrates suppression temperature of inhibited systems: III. salts and organic inhibitors

In Parts I and II, the Hu‐Lee‐Sum (HLS) correlation was developed and demonstrated to have an inherent generality and simplicity to predict structures I and II gas hydrates suppression temperature for both single and mixed salts systems. Utilization of thermodynamic hydrate inhibitors (THIs) is common practice in industry to prevent hydrate formation. Therefore, the HLS correlation is extended to predict hydrate suppression temperature with either single or mixed THIs, including any combination of inorganic salts and organic inhibitors. It is verified that hydrate equilibrium conditions with organic inhibitors also shows nearly independence of the water activity on temperature. In addition, additive contribution of salts and organic inhibitors to the water activity are used to determine the hydrate suppression temperature. A comprehensive comparison between the literature data and predicted results demonstrate the reliability of the HLS correlation for any combination of inorganic salts and organic inhibitors. © 2018 American Institute of Chemical EngineersAIChE J, 64: 4097–4109, 2018

Experimental evaluation of RAFT-based Poly(N-isopropylacrylamide) (PNIPAM) kinetic hydrate inhibitors

As the oil and gas industry produces hydrocarbons from deeper waters and colder regions the issue of hydrate formation becomes more serious. As a result, hydrate inhibition has focused on kinetic hydrate inhibitors (KHI) and anti-agglomerants (AA) as an alternative to the existing approaches which involves injecting vast quantities of thermodynamic inhibitors. In this research, we evaluated the effect of different architectures (linear and branched) of poly(N-isopropylacrylamide) (PNIPAM) polymers synthesized using reversible addition−fragmentation chain-transfer (RAFT) polymerization. Unlike non-reversible deactivation radical polymerisation (RDRP) synthetic routes this generates accurately controlled KHI candidates with target molecular weight, narrow molecular weight distributions and controlled architecture, so that the effect on hydrate inhibition can be more accurately assessed. The RAFT-based polymers (linear and branched) were compared to a commercially available linear PNIPAM synthesized via non-RDRP radical polymerization and control groups (pure water, PVP, and Luvicap). The hydrate experiments were performed in a high pressure autoclave with continuous cooling under different cooling rates (0.25 K/min, 0.033 K/min, and 0.017 K/min). In addition, a cold restart was simulated using constant subcooling. The results regarding subcooling temperature, onset time, and hydrate fraction with resistance-to-flow were compared to known KHIs. These revealed that a linear PNIPAM-MacroRAFT polymer delayed the hydrate nucleation with similar performance to known KHIs (eg., PVP and Luvicap). However, a branched polymer showed the best performance in terms of hydrate fraction and resistance-to-flow among all of the systems tested in this study. These data provide valuable information regarding linear and branched PNIPAM-MacroRAFT polymers by demonstrating their ability to delay hydrate formation but also in preventing hydrate agglomeration. These findings confirm that polymer architecture can effect hydrate inhibition.

A Study of Natural Proteins and Partially Hydrolyzed Derivatives as Green Kinetic Hydrate Inhibitors

One of the first ideas explored for kinetic hydrate inhibitors (KHIs) for oil industry applications came from observing that some animals contain antifreeze proteins (AFPs) that protect them from fatal ice crystal formation at subzero temperatures. However, AFPs, or ice-structuring proteins, are designed to prevent ice formation not hydrate formation. Therefore, although several AFPs are known to show some KHI activity, it is possible that other proteins or peptides may be even more effective as KHIs. We have now tested a range of readily available natural protein-based products from animal and plant sources as green KHIs, as well as an AFP that is used to make ice cream smoother. Experiments on nearly all of these products were conducted in a high-pressure titanium autoclave and also in steel rocking cells on a Structure II-forming gas mixture. The AFP gave the best performance, although this is at least in part due to some thermodynamic inhibition from salts and other chemicals present in the sample. So...

Hydrate Phase Equilibria for Methyldiethanolamine and Empirical Modeling for Prediction

The issue of gas hydrates in gas pipelines is commonly addressed by injecting hydrate inhibitors at the well heads. Alongside these inhibitors, other chemical additives are also injected to address various concerns such as to reduce the risk of corrosion and scaling. However, it is not clear how the combined chemical cocktail affects gas hydrate formation over a wide pressure range. Monoethylene glycol (MEG) and methyldiethanolamine (MDEA) are common chemicals that are usually used as part of hydrate inhibition and corrosion control programs respectively. Thus, in this study, the methane hydrate inhibition performance of MDEA in the presence and absence of MEG was assessed. The study produced new hydrate phase equilibria data at a high pressure range, suggesting MDEA performs as a thermodynamic hydrate inhibitor and thus enhances the hydrate inhibitory performance of MEG. Furthermore, because there does not appear to be any flow assurance prediction software that has the capability to simulate the effect of MDEA on hydrate formation, an algorithm that can accurately predict the equilibrium temperature of aqueous MDEA solutions with and without MEG was developed. The algorithm is based on the empirical modeling of the experimental data obtained in this study. This work will thus aid in the industrial application of hydrate inhibitors and improve gas hydrate prevention in production pipelines.

Cost-effective alkylammonium formate-based protic ionic liquids for methane hydrate inhibition

In light of current concerns about environmental impact, ionic liquids have been tested in a number of industrial applications, including gas purification, lubrication, and catalysis. In this work, cost-effective alkylammonium-based protic ionic liquids (PIL) were utilized as high-dosage gas hydrate inhibitors in order to achieve an inexpensive feedstock. Three structurally different PILs, ethylammonium formate ([EA][Of]), dimethylammonium formate ([DMA][Of]), and dimethylethylammonium formate ([DMEA][Of]), were studied to determine their inhibitory effect on methane gas hydrates. All of the studied PILs were initially tested for thermodynamic gas hydrate inhibition at 5 wt% and at 10 wt% to understand the effect of concentration by increasing the dosage. These PILs were produced by adding primary, secondary, and tertiary amines to formic acid, which is mildly acidic in nature and has biological significance. The PILs showed similar thermodynamic hydrate inhibition (THI) effects at the studied concentrations. The THI trend ([EA][Of] ≥ [DMA][Of] ≥ [DMEA][Of]) reflects the small effect of the structural variation of the cation, with the common formate anion providing the dominant inhibitory action due to presence of a carboxylic group. The pressure-temperature (P-T) equilibrium curve data of the investigated PILs were compared with the existing literature data for ILs including [TBMA][Of] at 10 wt% and 5 wt%. The comparison plots reveal that the THI effects of the studied PILs are better than or comparable to the other ILs, which is the matter of discussion over cost effective operation. Additionally, experimental kinetic hydrate inhibition (KHI) data were collected for 5 wt% PIL systems using polyethylene oxide (1 wt%) as an additive to demonstrate its synergistic effect.

Effects of ethanol on the performance of kinetic hydrate inhibitors

The main types of hydrate inhibitors are thermodynamic (THI), kinetics (KHI) and anti-agglomerants (AA) inhibitors. Kinetic inhibitors are used in low dosages but do not have satisfactory efficiency in large subcoolings. On the other hand, thermodynamic inhibitors are widely used in the industry and require high dosages. In order to study a combined inhibition, the behavior of three different commercial kinetic inhibitors combined with ethanol (THI) was tested under subcooling conditions in cases which unique kinetic inhibition did not yield satisfactory results. With 3% concentrations of kinetic inhibitors and a 10% by mass ratio of ethanol, it was possible to identify a significant increase in induction time for two of the inhibitors tested. Once the growth of the hydrate crystals began to appear, the presence of inhibitors did not result in significant gain in delaying the crystallization process. Some physical characteristics of the formed hydrates were altered in the presence of kinetic inhibitors and ethanol, evidencing a lower capacity of the crystals to adhere. With the same concentration of kinetic inhibitor and a 30% by mass ratio of ethanol the KHI presented low effectiveness.

Multiphase flash calculations for gas hydrates systems

In this study, the van der Waals and Platteeuw model was coupled with the Cubic Plus Association (CPA) equation of state (EoS) for equilibrium calculations in systems with gas hydrates. It has been applied to simple and complex multicomponent systems involving methane, ethane, propane, isobutane, carbon dioxide, nitrogen and hydrogen sulfide. Methanol, ethanol, monoethylene glycol, calcium chloride, sodium chloride and potassium chloride were contemplated as thermodynamic hydrate inhibitors. The calculations were performed in the presence of single and mixed inhibitors. The mole fraction of components in all phases were determined using flash algorithm procedures to improve the calculations accuracy. To evaluate the ability of the methodology, the prediction of hydrate phase behavior in the presence and absence of inhibitors was compared with the experimental data. Additionally, the binary interaction coefficients were considered as a linear function of temperature. Furthermore, the Langmuir constants were optimized for each gas hydrate former. The results obtained with the proposed approach agreed well with the experimental data, predominantly for hydrate systems comprising mixture of different inhibitors as salts and alcohols.

Experimental evaluation and thermodynamic modelling of AILs alkyl chain elongation on methane riched gas hydrate system

In this study, the thermodynamic inhibition of CH4 rich binary mixed hydrate system (70-30 mol% CH4 + CO2) is reported for four ammonium based ionic liquids (AILs) via experimental and modelling approaches. The T-cycle technique applied for the characterization of the AILs namely tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropyl ammonium hydroxide (TPrAOH) and tetrabutylammonium hydroxide (TBAOH). The hydrate liquid-vapour equilibrium (HLwVE) conditions of studied systems measure within the temperature and pressure ranges of 275.0–286.0 K and 3.0–7.50 MPa respectively at 10 wt% aqueous AILs solutions. All the studied AILs except TBAOH inflicted the THI influence by shifting the HLwVE of CH4 enrich mixed gas hydrates. Elongation in AILs alkyl chain length attributed to decrease the average hydrate suppression temperature (ΔŦ). At 10 wt%, TMAOH exhibited the maximum inhibition impact with a ΔŦ value of 1.28 K, followed by TEAOH (0.8 K), TPrAOH (0.7 K), and TBAOH (−0.84 K) respectively. Instead of hydrate inhibitor, TBAOH worked as gas hydrate promotor owing to the presence of relatively higher alkyl chain cation (butyl) make it semi-clathrate hydrate. The study further extended for different concentrations (1, 5 and 10 wt%) of TMAOH among the best considered AIL in this study. COSMO-RS investigation is also incorporated to further understand the thermodynamic inhibition behaviour of AILs via sigma profile analysis. Additionally, the enthalpies of hydrate dissociation for all studied AILs systems also calculated via Clausius-Clapeyron equation in this study. The calculated hydrate dissociation enthalpies data revealed that all the studied AILs except TBAOH show insignificant participation in mixed gas hydrate cage formation, therefore, do not form semi-clathrate hydrates. However, enthalpy data of TBAOH revealed that it participated in hydrate crystalline structure, therefore, worked as semi-clathrate hydrate. Furthermore, the HLwVE predictions of studied systems also performed via electrolyte based model proposed by Dickens and Quinby-Hunt and found in respectable agreement with the experimental data.

Effects of a naturally derived surfactant on hydrate anti-agglomeration using micromechanical force measurement

The performance of a hydrate anti-agglomerant (AA) on cyclopentane (CyC5) hydrate anti-agglomeration at various concentrations (0–1wt%, based on the oil phase) using MMF apparatus has been investigated. At low AA concentrations up to 0.01wt%, the AA reduces the cohesion force (capillary force) by reducing the CyC5-water interfacial tension. At concentrations higher than 0.1wt%, hydrate hydrophobicity alternation and AA’s thermodynamic inhibition effects are the main part of AA’s mechanism. Additionally, a “temporary agglomeration” phenomenon caused by surface melting of the hydrate particles is also observed, which may indicate the AA’s weak ability to produce stable water-CyC5 interface.

Assessing thermodynamic consistency of gas hydrates phase equilibrium data for inhibited systems

Phase equilibrium properties of gas hydrates in the presence of thermodynamic hydrate inhibitors (THIs) like alcohols, glycols, and salts are essential in developing thermodynamic prediction models to identify their physicochemical features and phase behavior for gas production from hydrates and operation of oil/gas production systems. Though a significant amount of experimental data are available in the literature and models have been developed based on those data, a reliable method to assess the thermodynamic consistency of the data has not been established. Here, we provide a rigorous method to assess the thermodynamic consistency of hydrate phase equilibrium data in inhibited systems. Fundamental thermodynamic relations are used to derive the assessment criteria for thermodynamic consistency, including the heat of dissociation for solid hydrate phase and the activity for liquid water. The quantitative assessment of CH4 hydrate + THIs, including salts, glycols, methanol, and amino acids are performed for demonstration, and guidelines on how to assess the thermodynamic consistency are provided.

Pressure drop in hydrate slurries: Rheology, granulometry and high water cut

Formation of gas hydrates in systems with high water content is one of the major challenges facing the petroleum industry today. Conventional mitigation using thermodynamic inhibitors is expensive due to large water volumes, while the most recent flow management strategies (anti-agglomerants, cold flow, etc.) have not yet been adopted because the dynamics of hydrate slurry are insufficiently understood. The present contribution examines a flow of gas, hydrates and water using computational fluid dynamics (CFD). The model couples the effective viscosity of gas-water slurry with the average size of hydrate agglomerates and the adhesive force that binds them. The model was validated against experimental pressure drop, demonstrating tolerable discrepancies. According to the simulations, onset of hydrate plugging is most probably related to the formation of a viscous bed at the gas-slurry interphase at hydrate concentrations slightly above 15%. A simplified theoretical approach is proposed for engineering estimates of pressure drop in the hydrate slurry pipes.

Toxicity evaluation of selected ionic liquid compounds on embryonic development of Zebrafish

Hydrate formation in seafloor pipelines is considered an economic and flow assurance issue for the oil and gas industries. Ionic liquids (ILs) have been recently used as potential hydrate inhibitors. Although branded as green compounds, their ecotoxicity in case of leakage from pipelines onto the aquatic environment needs more deep evaluations. Here, we investigate the impacts of three ILs previously used as successful thermodynamic hydrate inhibitors namely choline chloride (ChC1), 1-methyl-1-propyl pyrrolidinium triflate (PMPy [triflate]) and tetra-methyl ammonium acetate (TMAA). Mortality (including LC50), teratogenicity, locomotion and neurotoxicity, and hatching rate were utilized to investigate any potential acute toxicity of these ILs on embryonic development of zebrafish. No significant mortality or teratogenic effects were found for all tested compounds in a concentration range between 50 and 200 mg/L. The LC50 was significantly higher than the tested dose >200 mg/L. While, up to 200 mg/L all compound had no impact on the survival rate, ChCl showed a significant effect on neuromuscular development as judged by the increase of spontaneous tail coiling activity (25 VS 4 burst/ minutes of the negative control-treated embryos). Further, apart from PMPy [triflate], ChC1 and TMAA had a significant adverse effect on the hatching rate of the treated embryos at concentrations of 200 mg/L. However, this effect was very mild at lower concentrations (≤100 mg/L). Our data indicate that within the tested concentrations both TMAA and PMPy [triflate] had no or little potential harmful effect on embryonic development of aquatic fauna “green”, while ChC1 should be used with caution.